The three projects of this grant are highly focused on evaluating the PTEN/MMAC1 tumor suppressor gene and the phosphoinositide 3-kinase (PI3K) signaling pathway in prostate cancer. PI3K has been implicated in prostate cancer because of the recent discovery that PTEN encodes a phosphatase that hydrolyzes the lipid products of cancers have defects in PTEN. Prostate cancer cell lines that lack PTEN have constitutive activation of enzymes down-stream of PI3K, including the AKT protein- Ser/Thr kinase and reintroduction of PTEN (or addition of PI3K inhibitors) blocks this pathway and leads to decreased cell growth and increased apoptosis. Although studies with cell lines suggest that inhibition of PI3K should block growth and survival of tumors that result from loss of PTEN, there is no evidence that this is true in vivo. Heterozygous loss of PTEN in mice results in hyperplasia in multiple tissues, including prostate and adenocarcinomas of the prostate. These mice provide a model for human prostate cancers that result from loss of PTEN. The goal of the proposed work is to test the effect of deleting genes of enzymes in the PI3K pathway on the development of prostate cancer in mice, and to develop techniques that will evaluate whether the PI3K pathway is activated in human prostate cancers. The proposed work involves extensive collaborations between the three projects and the three cores, taking advantage of the expertise of individual laboratories. In Project 1, the Cantley laboratory will generate mice in which the regulatory subunits of PI3K are deleted in the prostate. These mice will then be crossed with the mice that lack PTEN in order to determine whether loss of the PI3k regulatory subunit blocks the development of prostate cancers that result from loss of PTEN. In Project 2, the Robert's laboratory will generate mice in which the catalytic subunit of PI3K is deleted in the prostate for the sample purpose. Multiple genes for both the regulatory and catalytic subunits of PI3K is deleted in the prostate for the same purpose. Multiple genes for both the regulatory and catalytic subunit of PI3K is deleted in the prostate for the same purpose. Multiple genes for both the regulatory and catalytic subunits of PI3K exist in mice and men and these studies will indicate which of these is the most critical for prostate cancer development. In Project 3, the Sellers laboratory will evaluate additional proteins downstream of PI3K. For downstream targets judged to be critical for PI3K-dependent growth or survival of prostate cancer cell lines, prostate-specific expression of dominant- negative forms or targeted deletion of the genes will be performed. Pharmaceutical companies are currently developing PI3K catalytic site inhibitors, AKT inhibitors and inhibitors of the function of the regulatory subunit of PI3K. However, to date, the inhibitors available are not sufficiently specific and have problems with bioavailability and toxicity that preclude evaluation. These studies will suggest which of these proteins should be targeted for treatment of prostate cancer.